FIG. 13 is a perspective view illustrating an input part of a conventional high frequency band IC chip (hereinafter referred to as a microwave IC chip) and a coplanar type prober, for explaining an input-output characteristic evaluating test for the conventional microwave IC chip. In the figure, reference numeral 1 designates a microwave IC chip. The IC chip 1 includes a GaAs substrate 10 on which a plurality of circuit elements, such as FETs (not shown), are present. A signal conductor 11 is disposed on the front surface of the substrate 10, and a metallized layer 10c for grounding is disposed on the rear surface of the substrate 10. The signal conductor 11 and the metallized layer 10c make a microstrip line 10A for sending microwave signals to the circuit elements. A signal pad 10a is disposed at an end of the signal conductor 11. Grounding pads 10b are disposed on opposite sides of the signal pad 10a and connected to the metallized ground layer 10c via through-holes (not shown). Reference numeral 90 designates a coplanar type wave guide prober. The prober 90 comprises a prober body 9 comprising an insulating substrate, a signal prober line 9a disposed on the surface of the prober body 9, and ground prober lines 9b disposed on opposite sides of the signal prober line 9a. Although FIG. 13 shows the input part of the microwave IC chip, an output part of the IC chip has the same structure as shown in FIG. 13.
A description is given of the operation.
The microwave IC chip 1 is put on a grounded stage (not shown), and the signal prober line 9a and the ground prober lines 9b of the coplanar type wave guide prober 90 are applied to the signal pad 10a and the ground pads 10b of the IC chip 1, respectively. In this state, microwave signals are input to the IC chip 1 to operate the IC chip 1, and the microwave signals output from the output part (not shown) are probed with a coplanar type wave guide prober having the same structure as the prober 90.
FIGS. 14, 15(a)-15(c ), and 16(a)-16(b) are diagrams for explaining a package used when a microwave IC chip is mounted on a mounting substrate. More specifically, FIG. 14 is a perspective view, partly broken away, illustrating external and internal structures of the package. FIG. 15(a) is a plan view illustrating a rear surface of the package, FIG. 15(b) is a side view of the package, and FIG. 15(c ) is a sectional view of the package taken along a line 15c--15c of FIG. 15(a). FIGS. 16(a) and 16(b) are a perspective view and a side view for explaining a method of mounting a microwave IC chip included in the package.
In these figures, reference numeral 500 designates a surface mountable package. The package 500 comprises a package body 501 having a surface on which a microwave IC chip 1 is disposed, and a lid 590 covering the IC chip 1. The package body 501 comprises a ceramic substrate 501a and a ground conductor layer 501b disposed on the rear surface of the ceramic substrate 501a. Portions of the ground conductor layer 501b are removed at opposite ends of the package to form U-shaped gaps 502a and 502b, whereby an input side coplanar line part 550 and an output side coplanar line part 560 are produced, respectively.
More specifically, a portion 552 of the conductor layer 501b surrounded by the U-shaped gap 502a serves as a coplanar signal conductor of the input side coplanar line part 550, and portions 551 and 553 of the conductor layer 501b on opposite sides of the portion 552 serve as ground conductors. Likewise, a portion 562 of the conductor layer 501b surrounded by the U-shaped gap 502b serves as a coplanar signal conductor of the output side coplanar line part 560, and portions 561 and 563 of the conductor layer 501b on opposite sides of the portion 562 serve as ground conductors. The width W of the coplanar signal conductor 552 (562) and the intervals G between the signal conductor 552 (562) and the ground conductors 551 and 553 (561 and 563) are chosen so that characteristic impedance of the coplanar line part 550 (560) is 50 .OMEGA..
The input side signal conductor 552 and the output side signal conductor 562 are connected to an input side signal lead 512 and an output side signal lead 522, respectively. The input side ground conductors 551 and 553 and the output side ground conductors 561 and 563 are connected to input side ground leads 511 and 513 and output side ground leads 521 and 523, respectively. An input side terminal 510 comprises the leads 511, 512, and 513, and an output side terminal 520 comprises the leads 521, 522, and 523. When the package 500 is mounted on a mounting substrate 601 (see FIG. 16(a)), the input and output terminals 510 and 520 are connected to coplanar lines 610 and 620 on the mounting substrate 601, respectively.
On the front surface of the ceramic substrate 501a, conductor layers 503a and 503b are disposed at positions opposite the coplanar signal conductors 552 and 562. The conductor layers 503a and 503b serve as strip signal conductors of input and output side microstrip line parts 570 and 580, respectively, and portions of the ground conductor layer 501b opposite the respective conductor layers 503a and 503b serve as ground conductors of the input and output side microstrip line parts 570 and 580, respectively, using the ceramic substrate 501a as a dielectric. The width of the strip signal conductor 503a (503b) and the thickness and dielectric constant of the ceramic substrate 501a are appropriately chosen so that the characteristic impedance of the microstrip line part 570 (580) is 50 .OMEGA.. The ceramic substrate 501a has through-holes 504a and 504b filled with a conductive material. The through-holes 504a and 504b connect the strip signal conductors 503a and 503b on the front surface of the ceramic substrate to the coplanar signal conductors 552 and 562 on the rear surface of the ceramic substrate, respectively.
A plurality of through-holes 505 filled with a conductive material are located in a region of the ceramic substrate 501a where the microwave IC chip 1 is disposed. When the IC chip 1 is disposed on that region of the ceramic substrate 501a, a ground conductor 1a of the IC chip 1 is connected to the ground conductor layer 501b on the rear surface of the package via the through-holes 505.
A description is given of a method of mounting the package 500 on the mounting substrate 601. Initially, the microwave IC chip 1 is adhered to the chip mounting region of the package body 501 with a conductive adhesive or the like, and input and output side electrode pads (not shown) on the surface of the chip 1 are connected to the input and output side strip signal conductors 503a and 503b by bonding wires 2a and 2b, respectively. Thereafter, the lid 590 is put on the package body 501 so as to cover the IC chip 1 and adhered to the package body with an adhesive or the like, whereby the IC chip 1 is hermetically sealed in the package 500.
Then, as illustrated in FIG. 16(a), the microwave IC package 500 is mounted on the mounting substrate 601. Preferably, a glass-epoxy substrate is employed as the mounting substrate 601. On a region of the mounting substrate 601 where the package 500 is to be disposed, a signal supply side coplanar line 610 for supplying microwave signals to the microwave IC chip 1 and a signal transmission side coplanar line 620 for transmitting the microwave signals from the IC chip 1 toward the latter stage are disposed. The signal supply side coplanar line 610 and the signal transmission side coplanar line 620 are connected to the input and output terminals 510 and 520 of the package 500, respectively.
More specifically, when the package 500 is put at a prescribed position of the mounting substrate 601, the signal lead 512 of the input terminal 510 of the package 500 contacts the signal conductor 612 of the signal supply side coplanar line 610 while the signal lead 522 of the output terminal 520 contacts the signal conductor 612 of the signal transmission side coplanar line 620. In addition, the ground leads 511 and 513 of the input terminal 510 contact the ground conductors 611 and 613 of the signal supply side coplanar line 610, respectively, while the ground leads 521 and 523 of the output terminal 520 contact the ground conductors 621 and 623 of the signal transmission side coplanar line 620, respectively. The respective contacting parts are fixed with solder or the like, whereby the microwave IC package 500 is mounted on the mounting substrate 601.
As illustrated in FIG. 16(b), another microwave IC package is mounted on the rear surface of the mounting substrate 601 in the same manner as described above. In this way, microwave IC packages are mounted on both surfaces of the mounting substrate 601, resulting in a high-density hybrid IC.
Meanwhile, Japanese Published Patent Application No. Hei. 2-106707 discloses a hybrid IC in which an end of a microstrip line on a mounting substrate is used as a terminal for an I/O interface with an external circuit.
In the high-frequency IC package 500 mounted on the mounting substrate 601, a microwave input applied to the input terminal 510 from the signal supply side coplanar line 610 on the mounting substrate 601 travels through the input side coplanar line part 550 on the rear surface of the package body and the through-hole 504a and reaches the input side microstrip line part 570 on the front surface of the package body. Further, the microwave input travels through the bonding wire 2a and reaches the microwave IC chip 1.
The microwave input is subjected to prescribed signal processing according to a function of the IC chip, for example, amplification, switching, or phase modification, and then it is output from the IC chip 1. The microwave output travels through the bonding wire 2b, the output side microstrip line part 580, and the through-hole 504b to reach the output side coplanar line part 560 on the rear surface of the package body. Then, it is output from the output terminal 520 of the package 500 to the signal transmission side coplanar line 620 of the mounting substrate 601.
The input-output characteristics of the microwave IC chip 1 are evaluated as described above. However, when the substrate 10 of the microwave IC chip 1 warps as shown in FIG. 13, the signal prober line 9a and the ground prober lines 9b of the prober 90 are not in perfect contact with the signal pad. 10a and the ground pads lob of the IC chip 1, respectively, so that a stable evaluation is not carried out.
Further, in the microwave IC package 500 shown in FIG. 14, the signal pad 10a and the ground pads 10b (see FIG. 13) of the IC chip 1 are connected to the strip line 503a (503b) by the wires 2a (2b). Since the wires 2a and 2b are not microwave transmission lines, dissipation due to unwanted radiation and reflection occurs at the ends of the wires. Further, the strip signal conductors 503a and 503b on the front surface of the ceramic substrate 501a are connected to the coplanar signal conductors 552 and 562 on the rear surface of the ceramic substrate 501a via the through-holes 504a and 504b filled with a conductive material, respectively. However, the through-holes 504a and 504b merely connect the signal conductors of the microstrip transmission lines on the opposite front and rear surfaces of the ceramic substrate, and a microwave transmission line structure comprising a signal conductor and ground conductors and having a matched characteristic impedance is not achieved. Therefore, dissipation due to unwanted radiation and reflection occurs at the ends of the through-holes.